1. Field of the Invention
This invention relates to a sheet holding cassette which is applicable to electrographic apparatuses, printing machines or the like and can supply sheets such as record sheets one by one from a stack of sheets enclosed in the cassette and composed of a number of superimposed sheets.
2. Description of the Prior Art
In an electrographic apparatus, printing machine or the like, if a number of sheets such as record sheets or the like are set beforehand, a sheet supplying device for supplying these sheets one by one has frequently been used. Such sheet supplying device has been classified into the following two devices. That is, a device for directly charging the sheets into a main body thereof and a second device which makes use of a cassette enclosing a stack of sheets therein and detachably mounted on the main body thereof. The second device has the advantage that it is particularly simple in operation.
A cassette for such sheet supplying device is composed of a rectangular box-shaped main body open at its top and provided at its upper front end corners with separating claws, respectively, and at its base with a sheet receiving plate loosely engaged with the main body. The sheet receiving plate is permitted to freely move up and down in the cassette. In addition, a base plate of the cassette is provided with openings through which is extended a projecting rod for moving the sheet receiving plate from the outside of the cassette.
When the cassette is mounted on the sheet supplying device, the main body is supported by a supporting member and the sheet receiving plate is supported by the projecting rod extending through the opening provided in the base plate. As a result, the sheets enclosed in the cassette are sandwiched between the separating claws and the sheet receiving plate. This condition is not changed even when the number of sheets, that is, the thickness of the stack of sheets becomes changed. The use of a sheet picking up roller ensures a positive supply of the sheets one by one. When the cassette is mounted on such sheet supplying device, the opening provided in the base of the cassette must be extended through the projecting rod. As a result, it is very difficult to charge the stack of sheets into the sheet supplying device. In addition, as the number of sheets is decreased, the position of the separating claws becomes lowered down, so that the sheet supplying position is changed, thereby changing the sheet transfer path. As a result, it is impossible to charge a large number of sheets into the sheet supplying device.
In another conventional sheet supplying device, the cassette mounted on the device is made stationary, while the projecting rod extending through the opening provided in the cassette base is made movable so as to upwardly urge the uppermost sheet of the stack of sheets against the sheet supply roller. In such conventional device, the position of the uppermost sheet of the stack of sheets is not changed irrespective of the change of the number of sheets. As a result, it is possible to eliminate the above mentioned disadvantage of the former device. But, when the cassette is removed from the device, the cassette must be disengaged from the projecting rod. In addition, the projecting rod must be constructed so as to be urged against the sheet receiving plate. As a result, such conventional device is also troublesome in operation and complex in construction.
In the above mentioned conventional devices, the sheet must be inserted beneath the separating claws when the stack of sheets is charged into the cassette, thereby rendering the charging operation of the stack of sheets into the cassette troublesome.